Maybe a stupid suggestion, but sometimes I forget to call the *SetFromOptions function on my object, and then get confused when changing the options has no effect. Just a thought from a fellow grad student.
Ellen On 10/16/2018 09:36 PM, Matthew Knepley wrote: > On Tue, Oct 16, 2018 at 9:14 PM Weizhuo Wang <[email protected] > <mailto:[email protected]>> wrote: > > I just tried both, neither of them make a difference. I got exactly > the same curve with either combination. > > > I have a hard time believing you. If you make the residual tolerance > much finer, your error will definitely change. > I run tests every day that do exactly this. You can run them too, since > they are just examples. > > Thanks, > > Matt > > > Thanks! > > Wang weizhuo > > On Tue, Oct 16, 2018 at 8:06 PM Matthew Knepley <[email protected] > <mailto:[email protected]>> wrote: > > On Tue, Oct 16, 2018 at 7:26 PM Weizhuo Wang > <[email protected] <mailto:[email protected]>> wrote: > > Hello again! > > After some tweaking the code is giving right answers now. > However it start to disagree with MATLAB results > ('traditional' way using matrix inverse) when the grid is > larger than 100*100. My PhD advisor and I suspects that the > default dimension of the Krylov subspace is 100 in the test > case we are running. If so, is there a way to increase the > size of the subspace? > > > 1) The default subspace size is 30, not 100. You can increase > the subspace size using > > -ksp_gmres_restart n > > 2) The problem is likely your tolerance. The default solver > tolerance is 1e-5. You can change it using > > -ksp_rtol 1e-9 > > Thanks, > > Matt > > > > Disagrees.png > > Thanks! > > Wang Weizhuo > > On Tue, Oct 9, 2018 at 2:50 AM Mark Adams <[email protected] > <mailto:[email protected]>> wrote: > > To reiterate what Matt is saying, you seem to have the > exact solution on a 10x10 grid. That makes no sense > unless the solution can be represented exactly by your > FE space (eg, u(x,y) = x + y). > > On Mon, Oct 8, 2018 at 9:33 PM Matthew Knepley > <[email protected] <mailto:[email protected]>> wrote: > > On Mon, Oct 8, 2018 at 9:28 PM Weizhuo Wang > <[email protected] > <mailto:[email protected]>> wrote: > > The code is attached in case anyone wants to > take a look, I will try the high frequency > scenario later. > > > That is not the error. It is superconvergence at the > vertices. The real solution is trigonometric, so your > linear interpolants or whatever you use is not going > to get the right value in between mesh points. You > need to do a real integral over the whole interval > to get the L_2 error. > > Thanks, > > Matt > > > On Mon, Oct 8, 2018 at 7:58 PM Mark Adams > <[email protected] <mailto:[email protected]>> wrote: > > > > On Mon, Oct 8, 2018 at 6:58 PM Weizhuo Wang > <[email protected] > <mailto:[email protected]>> wrote: > > The first plot is the norm with the flag > -pc_type lu with respect to number of > grids in one axis (n), and the second > plot is the norm without the flag > -pc_type lu. > > > So you are using the default PC w/o LU. The > default is ILU. This will reduce high > frequency effectively but is not effective > on the low frequency error. Don't expect > your algebraic error reduction to be at the > same scale as the residual reduction (what > KSP measures). > > > > > -- > Wang Weizhuo > > > > -- > What most experimenters take for granted before they > begin their experiments is infinitely more > interesting than any results to which their > experiments lead. > -- Norbert Wiener > > https://www.cse.buffalo.edu/~knepley/ > > <https://urldefense.proofpoint.com/v2/url?u=http-3A__www.cse.buffalo.edu_-7Eknepley_&d=DwMFaQ&c=OCIEmEwdEq_aNlsP4fF3gFqSN-E3mlr2t9JcDdfOZag&r=hsLktHsuxNfF6zyuWGCN8x-6ghPYxhx4cV62Hya47oo&m=EFM29ATgv4U8PjXEtfgMkuxKr5DGscMlH-j769W5W_4&s=grgSL2LaDCthvYvvFITmeOOWPCwgmNfYRPs94N8kmOs&e=> > > > > -- > Wang Weizhuo > > > > -- > What most experimenters take for granted before they begin their > experiments is infinitely more interesting than any results to > which their experiments lead. > -- Norbert Wiener > > https://www.cse.buffalo.edu/~knepley/ > <http://www.cse.buffalo.edu/%7Eknepley/> > > > > -- > Wang Weizhuo > > > > -- > What most experimenters take for granted before they begin their > experiments is infinitely more interesting than any results to which > their experiments lead. > -- Norbert Wiener > > https://www.cse.buffalo.edu/~knepley/ > <http://www.cse.buffalo.edu/%7Eknepley/>
